The present invention broadly relates to indexible stepping mechanisms for switches and, more specifically pertains to a new and improved construction of a push-button multi-position switch.
Generally speaking, the push-button multi-position switch of the present invention comprises a symbol or numeric drum or wheel, broadly simply referred to as a character drum or wheel, which is rotatably mounted in a switch housing and provided with contact elements and a drive pinion, and two individual actuation plungers arranged at both sides of the axle of the character drum or wheel and which are displaceable in the switch housing along an actuation path and against the force of a restoring spring. The two individual actuation plungers each comprise a switching or indexing arm and a latching or locking arm for the stepping or step-by-step drive of the character drum or wheel in both possible directions of rotation thereof, each such switching or indexing arm and each such latching or locking arm being provided to engage with their free ends at teeth of the drive pinion. The push-button multi-position switch further includes a locking or detent element which is displaceably guided at the switch housing in a direction substantially transverse to the predetermined direction of actuation of the two individual actuation plungers. This locking or detent element is movable by each individual actuation plunger into a locking position for the other individual actuation plunger.
In a multi-position switch known to the art as disclosed, for example, in German Published Patent Application No. 2,545,719, published April 14, 1977, each actuation plunger comprises a restoring spring which is a tension spring braced between the respective actuation plunger and the switch housing. The locking or detent element is guided as a movable separate part in a recess of the housing wall, which recess is located between the actuation plungers and extends substantially perpendicular to the direction of the working movement or stroke of the actuation plungers. This movable separate part coacts with a slanting or inclined surface provided at each actuation plunger. When both actuation plungers are non-operative, the locking or detent element must necessarily possess a certain clearance of motion such that the locking or detent element, upon actuating one actuation plunger, can lock the other inoperative actuation plunger only when the operative actuation plunger has been totally actuated, i.e. only after accomplishing the linear working movement or stroke and thus a complete switching or indexing step. Since it is therefore possible to simultaneously move both actuation plungers each by about one-half the actuation path or stroke, the possibility cannot be totally excluded that the character drum or wheel is thereby brought into and retained at an intermediate position, be this unintentional or not. However, this shortcoming or disadvantage is not acceptable in most applications of such multi-position switches. A further considerable disadvantage of this known multi-position switch is seen in the fact that the manufacture and, in particular, the assembly of the separate restoring springs and of the additional separate locking or detent element is labor-intense and time-consuming such that series or mass production of this known multi-position switch is complicated and this again increases its manufacturing costs.